The present invention relates to a diver""s information processing device. More particularly, the present invention is concerned with a technology for notifying a diver of a pressure decrease ratio at which pressure applied to a diver decreases during surfacing over diving for the purpose of minimizing the risk of the diver""s decompression sickness or excess pulmonary expansion at a high altitude at which a pressure change rate tends to increase.
A diver""s information processing device may be referred to as a so-called dive computer. A method of calculating the conditions for decompression after diving that is adapted to the diver""s information processing device is described in xe2x80x9cDive Computersxe2x80x94A Consumer""s Guide to History, Theory and Performancexe2x80x9d (Watersport Publishing Inc., 1991) written by Ken Loyst et al. Moreover, discussions have been made on a calculating method described in a theoretical literature xe2x80x9cDecompressionxe2x80x94Decompression Sicknessxe2x80x9d (Springer, Berlin, 1984, pp.14) written by A. A. Buhlmann.
Based on the theory, the diver""s information processing device calculates an amount of inert gas absorbed into a body and an amount of inert gas discharged therefrom during and after diving so as to grasp an amount of intracorporeal inert gas all the time. The diver""s information processing device is thus designed to minimize the risk of a diver""s decompression sickness.
Moreover, if a surfacing speed is too high, nitrogen or any other inert gas having permeated into a body becomes bubbles to cause decompression sickness. From a viewpoint of averting decompression sickness, it is important to observe a specific surfacing speed at which a diver should come up to the surface. In some conventional diver""s information processing devices, the surfacing speed is monitored. If a current surfacing speed is faster than the pre-set upper limit of a surfacing speed, a warning indicating that a specified surfacing speed is violated is generated to inform the diver of the fact.
Moreover, the surfacing speed may not be related to a change in hydraulic pressure occurring during surfacing. Specifically, in some diver""s information processing devices, a variation of a ratio of hydraulic pressure detected before surfacing to hydraulic pressure detected after surfacing, which is detected during a unit time, is taken into account. The upper limit of a surfacing speed is determined in association with each depth of water, and the surfacing speed is monitored.
However, these devices have a drawback that no consideration is taken into an atmospheric pressure on water in which diving is performed. A case where diving is performed at a high altitude at which the atmospheric pressure on water is low is compared with a case where diving is performed at a low altitude at which the atmospheric pressure on water is high. Consequently, it is revealed that even if a diver surfaces by the same distance at the same time instant in the water that exhibits the same concentration, a pressure change rate is smaller when diving is performed at the high altitude. Herein, the pressure change rate is a quotient of a pressure detected after the end of travel by a pressure detected before the start of the travel. However, the air in the lungs is inversely proportional to the pressure change rate, and is likely to expand more greatly than it is when diving is performed at the low altitude. When diving is performed at the high altitude, the risk of a diver""s decompression sickness or excess pulmonary expansion increases.
Nevertheless, although some diver""s information processing devices have the upper limit of a surfacing speed, at which surfacing is performed, set in association with a depth of water, many diver""s information processing devices have the upper limit of a surfacing speed set to a fixed value. No consideration is taken into the atmospheric pressure on water. From a viewpoint of putting emphasis on safety, the upper limit of a surfacing speed cannot help being set to a considerably small value. As a result, when diving is performed at a high altitude at which an atmospheric pressure on water is low, a warning indicating that a specified surfacing speed is violated is generated frequently, though the surfacing speed is tolerable. Therefore, information that does not match the current situation is provided. In contrast, when the upper limit of a surfacing speed is set to a large value in order to prevent incorrect generation of a warning, it is hard to reliably avert decompression sickness.
In consideration of the foregoing drawbacks, an object of the present invention is to provide a diver""s information processing device capable of setting the upper limit of a pressure decrease ratio, at which pressure decreases during surfacing, according to an atmospheric pressure on water in which diving is performed, and properly monitoring a surfacing speed during diving performed even at a high altitude at which the atmospheric pressure on water is low.
For accomplishing the above object, according to one aspect of the present invention, a diver""s information processing device comprises a pressure metering means, a diving time measuring means, a pressure decrease ratio calculating means, an upper limit-of-pressure decrease ratio setting means, and a pressure decrease ratio comparing means. The diving time measuring means measures a diving time. The pressure decrease ratio calculating means calculates a pressure decrease ratio, at which pressure decreases during surfacing, according to the pressure measured by the pressure metering means and the diving time measured by the diving time measuring means. The upper limit-of-pressure decrease ratio setting means sets the upper limit of a pressure decrease ratio. The pressure decrease ratio comparing means compares the upper limit of a pressure decrease ratio set by the upper limit-of-pressure decrease ratio setting means with the current pressure decrease ratio calculated by the pressure decrease ratio calculating means. The upper limit-of-pressure decrease ratio setting means sets the upper limit of a pressure decrease ratio, at which pressure decreases during surfacing within diving, according to information of an atmospheric pressure on water in which diving is performed.
According to the present invention, for monitoring whether a pressure decrease ratio at which pressure decreases during surfacing over diving is appropriate, the upper limit of a pressure decrease ratio is set to a predetermined value associated with an atmospheric pressure on water. What is referred to as the pressure decrease ratio is a quotient of a difference between a current absolute pressure and an absolute pressure detected t sec (min) earlier by a time t. The pressure decrease ratio is compared with the upper limit of a pressure decrease ratio that is associated with a current atmospheric pressure on water. For example, the upper limit of a pressure decrease ratio is set to a small value for diving performed at a high altitude at which the atmospheric pressure on water is low. This is because a change in absolute pressure, which is applied to a diver during surface per unit time is larger when diving is performed at a high altitude, at which the atmospheric pressure on water is low, than when diving is performed at a low altitude at which the atmospheric pressure on water is high. A variation per unit time of a ratio of an absolute pressure detected before start of surfacing to an absolute pressure detected thereafter has a more significant meaning than a decrease ratio at which a hydraulic pressure decreases during surfacing over diving. In Japanese Unexamined Patent Publication No. 10-250683, the upper limit of a surfacing speed is determined based on the current depth of water. Moreover, since the variation of the ratio of the absolute pressures detected before and after surfacing is taken into account, a mere surfacing speed is not employed but a pressure is adopted in order to monitor safety during surfacing. This is because the concentration of water is different from place to place, for example, the concentration of fresh water is different from that of seawater. Therefore, even when the surfacing speed is set to the same value, a change in pressure differs with the difference in the concentration of water. According to the present invention, the upper limit of a pressure decrease ratio is determined so that a relatively high pressure decrease ratio will be permitted during diving performed at a low altitude at which the atmospheric pressure on water is high, and only a relatively low pressure decrease ratio will be permitted during diving performed at a high altitude at which the atmospheric pressure on water is low. This makes it possible to properly judge safety during surfacing.
A pressure decrease ratio inferring means can be employed to infer a pressure decrease ratio from the rate of change of a pressure decrease ratio currently calculated by the pressure decrease ratio calculating means from a pressure decrease ratio previously calculated thereby.
When a diver surfaces rapidly during diving, the risk of the diver""s decompression sickness increases. Moreover, rapid surfacing releases pressure from the diver. This causes the air in the lungs to expand, and brings about a risk that the lungs may rupture. For averting this incident, since it is dangerous to give a warning when a surfacing speed comes to a dangerous level, notification must be performed before the surfacing speed rises to the dangerous level. For this purpose, the rate of change in the pressure decrease ratio must be checked, and a surfacing speed must be inferred from the change rate before the current surfacing speed rises to the dangerous level. By thus inferring a surfacing speed before a current surfacing speed rises to a dangerous level, greater safety can be guaranteed for a diver.
Preferably, the pressure decrease ratio inferring means infers a pressure decrease ratio from a rate of change of a currently calculated pressure decrease ratio from a previously calculated pressure decrease ratio until diving is completed. More preferably, during surfacing, a pressure decrease ratio in several seconds can be inferred sequentially.
Preferably, the upper limit-of-pressure decrease ratio setting means sets the upper limit of a pressure decrease ratio, at which pressure decreases during surfacing over diving, according to a pressure measured by the pressure metering means and a pre-set pressure change rate.
Herein, what is referred to as a pressure change rate is a quotient of an absolute pressure predicted in t seconds (minutes) by a current absolute pressure. Using the pressure change rate, the upper limit of a pressure decrease ratio can be determined based on the current pressure alone. This obviates the necessity of determining the upper limit of a pressure decrease ratio according to information of an atmospheric pressure on water or a current depth of water. Consequently, the number of processing steps decreases.
A pressure decrease ratio notifying means can be used to notify the diver of a current pressure decrease ratio. Otherwise, when it is judged from comparison of a current pressure decrease ratio with the upper limit of a pressure decrease ratio that the current pressure decrease ratio is larger than the upper limit, the pressure decrease ratio notifying means gives a warning.
When the pressure decrease ratio continuously exceeds a notification level, the notifying means given a warning. This makes it possible to sensuously grasp whether a pressure decrease ratio currently tends to increase or decrease. Before the pressure decrease ratio reaches a dangerous level, danger can be readily reported to a diver.
A pressure decrease ratio may be reported by continuously varying the notification level that is indicated with an alarm sound of a varying frequency. A continuous change in the pressure decrease ratio may thus be expressed. It can be sensuously grasped whether the pressure decrease ratio currently tends to increase or decrease. Before the pressure decrease ratio reaches a dangerous level, danger can be readily reported to a diver. Moreover, in particular, when the pressure decrease ratio approaches to the dangerous level, if the frequency of the alarm sound increases, a diver can intuitively recognize an impending danger.
Moreover, since a notification level is continuously varied and indicated with an alarm sound of a varying tempo in order to tell a current pressure decrease ratio, a continuous change in the pressure decrease ratio can be expressed. Consequently, a diver can intuitively grasp whether the pressure decrease ratio currently tends to increase or decrease. Before the pressure decrease ratio reaches a dangerous level, danger can be readily communicated to a diver. Moreover, if the tempo of the alarm sound increases when the pressure decrease ratio approaches the dangerous level, similarly to a case that his/her heart rate increases when a human being is in danger, a diver can intuitively recognize that he/she is in danger.
Furthermore, when the notification level is continuously varied and indicated with an alarm sound of a varying tempo in order to notify a diver of a current pressure decrease ratio, a continuous change in the pressure decrease ratio can be expressed. Consequently, a diver can intuitively grasp whether the pressure decrease ratio currently tends to increase or decrease. Before the pressure decrease ratio reaches a dangerous level, danger can be readily told to a diver. Moreover, when the pressure decrease ratio approaches the dangerous level, if the volume of the alarm sound increases, a diver will more seriously recognize that he/she is in danger. This would be effective in attracting a diver""s attention.
Moreover, the notification level may be continuously varied and indicated with a vibratory alarm of a varying amplitude or tempo. When the vibratory alarm is used in this way, unlike when the alarm sound is adopted, a diver will not confound with a warning given to himself/herself and a warning given to any other diver. The diver can therefore recognize in an earlier stage that information of a pressure decrease ratio is addressed to himself/herself. This would be effective in preventing the pressure decrease ratio from reaching a dangerous level. Moreover, if the tempo of the vibratory alarm increases when the pressure decrease ratio approaches the dangerous level, similarly to a case that his/her heart rate increases when a human being is in danger, a diver can intuitively recognize that he/she is in danger.
An upper limit-of-pressure decrease ratio indicating means can be employed to indicate a tolerance of a pressure decrease ratio to the upper limit of a pressure decrease ratio. The employment of a display unit for visual recognition is an effective means for notifying a diver of danger implied with the pressure decrease ratio. When the display unit and notifying means described in claim 1 to claim 5 are used in combination, danger can be more readily told to a diver.
Any of the above combinations will do as long as danger is notified and reported to a diver in an easy-to-understand manner.